1. Field of the Invention
The present invention relates to a projection display apparatus and method, and more particularly, to a projection display apparatus including a modulation light source and a transmission-type screen.
2. Description of the Related Art
A projection display apparatus is used to display an image on a screen using a laser light source. Unlike, a cathode ray tube (CRT) display and a plasma display panel (PDP), the projection display apparatus is a non-light emission display apparatus and includes a light valve for adjusting the amount of light based on an image signal, an illumination optical system for illuminating the light valve with illumination light from a light source, and a projection optical system for enlargedly projecting a small image formed by the light valve onto a large screen.
The projection display apparatus is classified into a rear projection type for projecting image light onto a screen from the rear side of the screen as viewed from a viewer and a front projection type for projecting image light onto the screen from the front side of the screen as viewed from the viewer. As shown in FIG. 1, a transmission-type screen 29 used for the rear projection type includes a Fresnel lens screen (Fresnel optical element) 2 for bending image light 16 from a projector 1 to a viewer 8 side and a light diffusing means 3 for diffusing the image light in a predetermined dispersion angle range. In FIG. 1, reference numeral 4 denotes a Fresnel lens substrate, 5 denotes a light exit side Fresnel lens, 6 denotes a lens component, and 7 denotes a light diffusion sheet. The Fresnel lens screen 2 (Fresnel optical element) includes the Fresnel lens substrate 4 and the light exit side Fresnel lens 5. The light diffusing means 3 includes the lens component 6 and the light diffusion sheet 7. In addition, in FIG. 1, reference numeral 9 denotes a light valve, 10 denotes a projection optical system, 11 denotes a illumination optical system, and 22 denotes a light source. The projector 1 includes the light source 22, the illumination optical system 11, the light valve 9, and the projection optical system 10. Further, in FIG. 1, reference numeral 17 denotes a reflecting mirror.
For example, when light from a light source whose light emission area and beam divergence point is small, such as a laser, is focused by an optical system represented by a lens or a mirror, a focused spot becomes very small, so a light energy per unit area increases. Therefore, the projection display apparatus is designed such that, in a normal use mode, the amount of light from a high-power laser serving as an incorporated light source is adjusted by intensity modulation or time modulation of the light source using a movable aperture (not shown) of the illumination optical system 11 and the light valve 9 and the light beam is spread by the projection optical system 10 and distributed over a solid angle by the transmission-type screen 29. Thus, irradiance (light energy per unit area per unit time) and radiant exposure (light energy per unit area) become sufficiently small. A function or interlock for preventing erroneous manipulation or operation of a viewer is provided.
One of conventional examples is an example in which, in an image display apparatus for displaying an image on a screen using a high-energy laser as a laser light source, abnormality caused by the light source is detected. This is that, in order not to hinder viewing, an optical sensor represented by a photodiode is provided outside an effective screen area (display area) on the screen, whether or not the abnormality of the laser light source is caused is detected based on an output of the optical sensor, and generated laser light is stopped, reduced in amount, or blocked when it is determined that the abnormality is caused (see, for example, JP 2000-267621 A).
In the conventional projection display apparatus, the optical sensor is located outside the effective screen area (display area) on the screen, so it is possible to detect a state in which the screen is detached (together with the optical sensor), a state in which an alignment deviation in the projection optical system occurs, and a state in which the output abnormality of the laser light source. However, there is a problem that a light output cannot be detected within the effective screen area (display area). In addition, there is a problem that it is impossible to detect overturning or vibration of the display apparatus, cracking, disassembly, deformation, or breakage of a case or of a screen portion located on the effective screen area (display area), or the like.
In the external appearance of the projection display apparatus, there is a large window for providing, in a case 28 (see FIG. 6), the transmission-type screen 29 for displaying an image to the viewer 8, except small windows required for a ventilation opening, a wiring, and the like. When the transmission-type screen 29 is provided in the case 28, a space is obtained in an inner portion of the projection display apparatus by the case 28 and the transmission-type screen 29. Therefore, the projection display apparatus is divided into an outer portion of the apparatus (hereinafter referred to as an exterior) and the inner portion of the apparatus (hereinafter referred to as an interior) by using the case 28 and the transmission-type screen 29 as boundaries.
In a normal use mode, it is preferable to detect a leakage of light (abnormality of light output) to the exterior. When the viewer 8 disassembles, breaks, or deforms the case 28 and the transmission-type screen 29, the viewer 8 may go to the interior of the case 28. Even in a mode except the normal use mode, it is preferable to detect such abnormality quickly before image is displayed and to stop or block generated illumination light, thereby preventing the leakage of light.